This invention relates to rotary shaft decoupling devices and more particularly to an improved shaft decoupler device of the type that can be actuated to rapidly decouple a driven apparatus, such as a generator, from its prime mover.
While not limited thereto, the present invention finds application in association with aircraft generators wherein it is desirable for the flight engineer to be able to positively decouple a generator from the aircraft engine, and to be assured that recoupling will not occur. Heretofore, a shaft decoupler has been used that compirsed a grooved input component, an axially aligned grooved output component, a plurality of cylindrical keys or rollers, and an outer component or retainer. The rollers are normally held in the grooves of the driving and driven components by the outer component or retainer and the entire combination rotates as a unit. Upon actuation, a plunger engages a pin on the periphery of the outer component, momentarily arresting its rotation and allowing the driving and driven components to index to a position relative to the outer component where the grooves and rollers align with recesses in the outer component. Radial restraint on the rollers is thereby relieved and the rollers move from the grooves into the outer component recesses where they are held by centrifugal force. The driving and driven components are thereby freed for relative rotation and the generator is no longer driven.
Although all of the force transmitting decoupler components have been formed of high strength steel and thrust and journal bearings of brass or bronze, all carefully selected for proper fit, finish, and material hardness, the components have been subject to severe and rapid fretting wear and failure. Frequently during service the shaft decoupler components became so inhibited due to wear and the build-up of fretting corrosion deposits that the decoupler failed to actuate when required. In other cases wear progressed to the extent that the decoupler actuated unintentionally. The wear occurs due to the cyclic loading of the generator which produces torsional oscillations in the coupling, and also due to axial and flexural stresses imposed by misalignment inherent in the generator gearbox installation.
Another problem that has been encountered with existing decouplers of the foregoing type has been that of inadvertent resetting, or engagement, of the decoupler, as has resulted on the occasion of reverse rotation of the driving shaft component within the outer component and a resultant deposition of two rollers in one recess, the two rollers jamming and effecting a driving situation.